The main problem with a lot of big releases these days is that to meet the initial demand all cylinders in the factorys are geared towards the kit bits.
If the kit is late people complain, if the kit is released in small number people complain.... at the end of the day people ideally want everything yesterday and its hard to meet that sort of deadline
Also companies, even big ones like AE, have to circulate their money carefully. It costs a certain amount to build each kit, if they run 5000 kits off in bulk it is a large outgoing in one go, this is why they then have to re-coup some of that money back from sales to pay for the next bulk manufacture. Normally the kits take preference, hence the spares delay.
With regards to FT releases, although I will admit marketing is part of the reason for the delayed release the other important reason is they like to fully test the kit to make any improvements before they release the full competition kit. As far as I know a lot of the AE Team drivers have input on what they want in their cars and this often dictates what ends up in the FT kit. Also small improvements, like moulding errors etc.. are normally found out in the first 6 months of a car's release and these will be fixed for the FT version.
The main problem with spares is that manufacture in the early stages is geared towards kit parts, this ties up the machines and finances for spares production.
AE, HPI. Losi and all the RC manufacturers have to try to meet demands of the customers, now you can argue some methods used work better than others but that is a different discussion. it is hard to please everyone. Imagine if AE said the TC4 is going to be delayed 3 months to ensure a full supply of spares is available for the kit release. There would be tons of people on here complaining that they should release it first.
Its one of those endless no win situations that happen in every business.